TITLE:   GCN CIRCULAR
NUMBER:  5733
SUBJECT: GRB061019: Swift XRT refined analysis
DATE:    06/10/19 16:19:29 GMT
FROM:    Cristiano Guidorzi at INAF-OAB  <cristiano.guidorzi@brera.inaf.it>

C. Guidorzi, P. Romano (Univ Bicocca & INAF-OAB), A. Moretti (INAF-OAB)
on behalf of the Swift-XRT team:

We have analysed the first 3 orbits of Swift-XRT data of GRB 061019
(Guidorzi et al., GCN Circ. 5728). The data set consists of 6.5 ks in
Photon Counting (PC) mode.

We derived an XRT refined position of:

RA(J2000)  = 06h 06m 30.73s
Dec(J2000) = 29d 34' 10.5''

with an estimated error radius of 6.7 arcsec (90% containment, including
boresight uncertainties). This lies 4.2 arcsec from the preliminary XRT
position (Guidorzi et al., GCN Circ. 5729) and 88 arcsec from the
ground-refined BAT position (Sakamoto et al., GCN Circ. 5732).
The XRT refined position is still within the BAT error circle.
The K-band candidate reported by Covino et al. (GCN Circ. 5730) lies
within the refined XRT error circle, 3.2 arcsec from our new position.

The X-ray lightcurve shows an initial slope of 0.7 +/- 0.4, with possible
break around 10^4 s after the burst to an almost flat decay.
Alternatively, it can be fit with a single power law with slope 0.56 +- 
0.10.
Further data will help clarify this ambiguity.

The time-averaged spectrum (from T+2.8 ks to T+17 ks) can be fit with an
absorbed power-law with a photon index of 2.1 +/- 0.3 (90%) and an 
absorption
column of (9 +/- 2)e21 cm^-2 (90%), significantly in excess of the Galactic
value in the direction of the burst (4.8e21 cm^-2).
The mean observed (unabsorbed) flux in the 0.3-10 keV energy band is
4.2e-12 (9.2e-12) erg cm^-2 s^-1.

Assuming the single power-law decay, the count rate at T+24 h
is predicted to be 1.6e-2 cts s^-1, corresponding to an unabsorbed
0.3-10 keV flux of 2.2e-12 erg cm^-2 s^-1.

This circular is an official product of the Swift-XRT team.